The preferred fuel is Natural Gas (NG)
as it is plentiful (in USA), cost effective, clean and compressible by the
engine. Instead of having to pay $1.5 to compressed NG with a pump
(amortized maintenance costs of a "Phil" pump, for example), the engine
will do it with minimal cost.
There is no detonation issues with fuels due to many factors. Initial
burn temperatures can be controlled and varied to meet different fuel
characteristics. Liquid fuels are generally mixed with gaseous.
Due to the 4 times increase in fuel economy, there is no "range anxiety"
in vehicle applications with current tank sizes. A small car would
have at least an 800 mile range on NG whereas with current piston crank
engines the range would be 200 miles, which is not enough to make NG
All the NG fuel tanks are included with the engine making every engine able to access NG from their house or business.